International Patent Application Publication Number WO 2006/110157 and International Patent Application Publication Number WO 2006/015261 provide phosphonamidate derivatives of (2R′,5R′)-9-(3-fluoro-2,5-dihydro-5-phosphonomethoxy-2-furanyl)adenine that are reported to be useful as anti-HIV agents. Compound 13 is one such derivative.

International Patent Application Publication Number WO 2010/005986 provides salt forms of compound 13 including the citrate salt (compound 14) which are also reported to be useful as anti-HIV agents.

There is currently a need for improved methods for preparing certain compounds reported in International Patent Application Publication Numbers WO 2006/110157, WO 2006/015261 and WO 2010/005986. In particular, there is a need for new synthetic methods that are simpler or less expensive to carry out, that provide an increased yield, or that eliminate the use of toxic or costly reagents.